The present invention relates to a method of controlling supply of working fluid for an ordinary machine or a construction machine. The invention also relates to a control device used for such a method.
FIG. 3 shows an example of a hydraulic excavator as a construction machine. The hydraulic excavator has a lower structure 1 and an upper structure 3, which is revolvably attached to the lower structure 1 with a revolving bearing portion 2 therebetween. A front attachment 4 is mounted on the upper structure 3. The front attachment 4 includes a boom 5, an arm 6 and a bucket 7. The base end of the boom 5 is rotatably fitted to the upper structure 3, while the front end of the boom 5 is rotatably attached to the base end of the arm 6. The bucket 7 is rotatably attached to the front end of the arm 6. The boom 5, the arm 6 and the bucket 7 are adapted to be rotated by a boom-cylinder 5c, an arm cylinder 6c and a bucket cylinder 7c respectively.
An example of conventional swing priority circuits is shown in FIG. 4, wherein working fluid is discharged from a hydraulic pump 10. The working fluid is then divided and fed into a center bypass line 13 and a parallel line 14 in a control valve 12, with a relief valve 11 controlling the pressure of the working fluid to a preset pressure.
A throttling selector valve dedicated to swinging motion (hereinafter called the swing selector valve) 15, an arm-dedicated throttling selector valve (hereinafter called the arm-dedicated selector valve) 16, and other throttling selector valves 28,29 are disposed in the control valve 12. The swing selector valve 15 is adapted to control a revolution motor 3m for revolving the upper structure to the right or the left. The other throttling selector valves 28,29 are adapted to control other cylinders of the front attachment 4 and the drive motor of the lower structure 1.
The swing selector valve 15 is designed to be pilot-operated by a remote-control valve dedicated to controlling hydraulic pressure for swinging motion and adapted to be manually operated with a swing operating lever. The arm-dedicated selector valve 16 is designed to be pilot-operated by an oil pressure remote-controlling valve that is dedicated to controlling the arm and adapted to be manually operated with another operating lever.
The swing selector valve 15 is disposed upstream from the arm-dedicated selector valve 16, and a supply line 17 that leads to the swing selector valve 15 is connected to the parallel line 14, thereby forming a so-called parallel circuit.
A supply line 18 leading to the arm-dedicated selector valve 16 is connected to the center bypass line 13, thereby forming a so-called tandem circuit.
A supply line 19 extends between the parallel line 14 and the supply line 18, and a swing priority valve 21 is disposed in the supply line 19. The swing priority valve 21 is adapted to be changed over based on external pilot signal pressure fed from a solenoid valve 20, which is of an on/off switching type. When the solenoid valve 20 is off, the external pilot signal pressure that is fed from a pilot pump 22 through the solenoid valve 20 is applied through a pilot line 23 to the swing priority valve 21 and switches said swing priority valve 21 so that the parallel line 14 communicates with the supply line 18. When the solenoid valve 20 is at the xe2x80x98onxe2x80x99 position, the pilot line 23 communicates with a drain line 24 so that the swing priority valve 21 is at the neutral position as shown in the drawing. Therefore, the parallel line 14 and the supply line 18 are cut off from each other.
When the solenoid valve 20 is switched on, the working fluid is fed to the arm cylinder 6c solely from the center bypass line 13, because the supply line 19 is blocked by the swing priority valve 21, which is at the neutral position.
Therefore, when the revolution motor 3m operates in sync with the arm cylinder 6c, the working fluid fed to the arm cylinder 6c is limited by means of a bypass notch 25 of the swing selector valve 15, and the working fluid fed to the revolution motor 3m, which serves to revolve the upper structure 3, travels from the parallel line 14 to the arm cylinder 6c through the supply line 17 and a supply notch 27.
In other words, the fluid is preferentially fed to the swing system. This mechanism is a so-called swing priority circuit, which is particularly effective for, for example, digging a groove by conducting an arm-in operation while pushing the bucket against the wall of the groove with revolving motion.
When the solenoid valve 20 is turned off, the external pilot signal pressure fed from the pilot pump 22 changes over the swing priority valve 21 so that the parallel line 14 communicates with the supply line 18. Therefore, if the solenoid valve 20 is at the xe2x80x98offxe2x80x99 position when the revolution motor 3m operates in sync with the arm cylinder 6c, swing priority does not work, because the parallel line 14 feeds working fluid to the arm cylinder 6c. 
According to the prior art described above, the manner of controlling the swing priority valve 21 is on/off control by the solenoid valve 20. Therefore, as described above, in case the swing priority valve 21 is in the blocked state in the swing priority circuit, the bypass notch 25 of the swing selector valve 15 limits the working fluid during the period when the revolution motor 3m operates in sync with the arm cylinder 6c. Along the nearly entire stroke of the swing selector valve 15, the opening-area of the bypass notch 25 is normally much smaller than the opening-area of the bypass notch 27 as shown in FIG. 5 so as to ensure a sufficient supply of working fluid to the revolution motor 3m during swinging operation.
As a result, in cases where there is a change in the degree of operation of the swing operating lever, in other words the distance of shifting the swing selector valve 15, the working fluid fed through the supply line 18 to the arm-dedicated selector valve 16 is considerably reduced by the bypass notch 25 almost regardless of the degree of operation of the swing operating lever. Thus, the working fluid fed to the arm cylinder 6c is reduced to an extremely small quantity.
The way a machine is supposed to work is that when the degree of operation of the swing operating lever is increased, the quantity of the hydraulic fluid supplied to the arm cylinder 6c should increase accordingly. Likewise, when the degree of operation of the swing operating lever is reduced, the quantity of the hydraulic fluid supplied to the arm cylinder 6c should decrease accordingly. In other words, it is desirable that the working fluid fed from the hydraulic pump 10 be effectively and efficiently used. In reality, however, it is difficult with the conventional art to achieve effective use of working fluid. During minute swinging operation, too, the conventional art presents a problem in that large restriction at the bypass notch 25 hinders quick movement of the arm cylinder 6c. 
In order to solve the above problem, an object of the present invention is to make effective use of working fluid fed from a pump to a plurality of throttling selector valves. Another object of the invention is to make the machine more convenient to operate by ensuring smooth interactive operation among a plurality of hydraulic actuators.
A method of controlling supply of working fluid according to the present invention calls for feeding working fluid from a pump to a plurality of throttling selector valves adapted to respectively control a plurality of hydraulic actuators in such a manner that the working fluid flows through the throttling selector valves in sequence, while feeding working fluid from the pump to one located relatively upstream of the throttling selector valves, i.e. the first throttling selector valve, without passing through any other throttling selector valves and feeding working fluid from the pump to another one located relatively downstream of the throttling selector valves, i.e. the second throttling selector valve, without passing through any other throttling selector valves in such a manner that the quantity of the working fluid fed to the second throttling selector valve is throttle-controlled according to the degree of operation of the first throttling selector valve. According to the structure described above, when the degree of operation of the first throttling selector valve increases, the quantity of the working fluid supplied to the second throttling selector valve is reduced accordingly so that the working fluid fed from the pump is efficiently distributed to the hydraulic actuator controlled by the first throttling selector valve and the hydraulic actuator that is controlled by the second throttling selector valve. Furthermore, even when the first throttling selector valve operates, the structure described above prevents radical change in quantity of the hydraulic fluid fed to the second throttling selector valve, thereby ensuring smooth interactive operation among a plurality of hydraulic actuators and consequently making the machine more convenient to operate.
According to another feature thereof, the invention relates to a method of controlling supply of working fluid in a construction machine having a plurality of hydraulic actuators that comprise at least actuators of a revolving system and actuators of a working equipment system, said method calling for feeding working fluid from a pump to a plurality of throttling selector valves adapted to respectively control the aforementioned plurality of hydraulic actuators in such a manner that the working fluid flows through the throttling selector valves in sequence, while feeding working fluid from the pump to one of the throttling selector valves, i.e. a throttling selector valve located relatively upstream and dedicated to the revolving system, without passing through any other throttling selector valves and feeding working fluid from the pump to another one of the throttling selector valves, i.e. a throttling selector valve located relatively downstream and dedicated to the working equipment system, without passing through any other throttling selector valves in such a manner that the quantity of the working fluid fed to the throttling selector valve dedicated to the working equipment system is throttle-controlled according to the degree of operation of the throttling selector valve dedicated to the revolving system. According to the structure described above, when the throttling selector valve of the revolving system of a construction machine such as a hydraulic excavator is minutely operated, a sufficient quantity of working fluid is fed to the throttling selector valve dedicated to the working equipment system so that the working equipment can quickly be moved while minute revolution is underway. Thus, the construction machine is made more convenient to operate.
A working fluid supply control device according to the invention includes a pump adapted to discharge working fluid; a plurality of hydraulic actuators adapted to be operated by the working fluid; a plurality of throttling selector valves for respectively controlling the working fluid fed from the pump to said plurality of hydraulic actuators; a center bypass line for sequentially supplying said plurality of throttling selector valves with the working fluid discharged from the pump; a parallel line for independently supplying said plurality of throttling selector valves in sequence with the working fluid discharged from the pump; a supply line branching off from the center bypass line at a point between the first throttling selector valve, which is one of the aforementioned throttling selector valves, and the second throttling selector valve, which is a separate and different one of the throttling selector valves and located downstream from said first throttling selector valve, said supply line connected to a supply port of the second throttling selector valve; a separate and different supply line branching off from the parallel line and connected to the supply port of the second throttling selector valve; a priority valve disposed in the aforementioned separate and different supply line and designed such that the degree of opening-area of the priority valve can be so adjusted as to give priority to the quantity of the hydraulic fluid fed to the first throttling selector valve over the quantity of the hydraulic fluid fed to the second throttling selector valve; and a control means adapted to steadily adjust the priority valve from the fully open state to the fully closed state in accordance with degree of operation of the first throttling selector valve. With the structure as above, even when the hydraulic fluid fed from the center bypass line through one supply line, i.e. the earlier mentioned one of the two supply lines, to the supply port of the second throttling selector valve is reduced with the center bypass line throttled down by operation of the first throttling selector valve, the quantity of the hydraulic fluid fed from the parallel line through the other supply line to the supply port of the second throttling selector valve is automatically controlled by the priority valve that is steadily adjusted from the open state to the closed state by the control means according to degree of operation of the first throttling selector valve. Thus, the working fluid fed from the pump can efficiently be utilized as it is completely distributed to the hydraulic actuator controlled by the first throttling selector valve and the hydraulic actuator controlled by the second throttling selector valve, while radical change in the quantity of working fluid fed to the second throttling selector valve is prevented from occurring during operation of the first throttling selector valve. Therefore, a device according to the invention ensures smooth interactive operation among a plurality of hydraulic actuators and makes the machine more convenient to operate.
According to yet another feature of the invention, the aforementioned first throttling selector valve of the working fluid supply control device is a swing-dedicated throttling selector valve for controlling swinging motion of a hydraulic excavator; the second throttling selector valve is an arm-dedicated throttling selector valve for controlling action of the arm of a hydraulic excavator; and the priority valve is a swing priority valve for giving priority to swinging motion over action of the arm. With the structure as above, a sufficient quantity of working fluid can be fed through the swing priority valve to the arm-dedicated throttling selector valve of the hydraulic excavator when the swing-dedicated throttling selector valve is minutely operated. Therefore, the structure described above makes the hydraulic excavator more convenient to operate, because the hydraulic actuator for the arm can be moved rapidly even during minute swinging operation.
According to yet another feature of the invention, the swing priority valve of the working fluid supply control device is a pilot-operated throttle valve which is adapted to gradually open from the fully closed position, where the spring is at the return position, in accordance with increase of external pilot signal pressure; and the control means is a pilot-operated pressure reducing valve adapted to be controlled in such a manner that its outlet pressure, which serves as external pilot signal pressure applied to the priority valve, is reduced according to increase in remote control pressure for pilot-operating the first throttling selector valve. With the structure as above, the outlet pressure of the pilot-operated pressure reducing valve serving as the control means is reduced according to increase in remote control pressure for pilot-operating the first throttling selector valve, and the outlet pressure serving as an external pilot signal pressure works on the pilot-operated throttle valve serving as the priority valve so that the priority valve is gradually closed from the fully open state to the fully closed state, where the spring is at the return position, in accordance with reduction of the external pilot signal pressure. By solely using an inexpensive pilot pressure circuit, the structure described above is capable of controlling distribution of an appropriate quantity of hydraulic fluid from the priority valve to the second throttling selector valve in accordance with degree of operation of the first throttling selector valve.